New monocyclic pentaoxyphosphoranes 1-4,6 and the furanosyl derivative, 7, were synthesized from the reaction of tris(2,6-dimethylphenyl) phosphite (5) with a diol or a quinone. The pentacoordinated derivatives 1-4 were studied by X-ray analysis and represent the first structurally chartacterized monocyclic oxyphosphoranes that have six-, seven-, and eight-membered rings. All possess trigonal-bipyramidal geometries with the rings spanning apical-equatorial positions. Retention of these structures in solution is indicated by 'H, l3C, and 3IP NMR. Twist-boat, rowboat, and distorted-tub conformations are found for the six-(1), seven-( 2), and eight-(4) membered ring derivatives, respectively. Phosphorane 3 has a more planar phosphorinane ring, a consequence of ring unsaturation. Variable-temperature *H and 13C NMR establish nonrigid behavior supporting a simple Berry pseudorotation in which the rings exchange apical-equatorial positions. It is concluded that six-membered rings of pentaoxyphosphoranes prefer apical-equatorial sites of a TBP. The preferred conformation of saturated six-membered rings is generally that of a boat. Phosphorane 1 crystallizes in the monoclinic space group C2/c with a -29.392 ( 8), b = 11.420 (5), c = 16.379 (2) Á, ß = 92.22 (1)°, and Z = 8. Compound 2 crystallizes in the monoclinic space group P2{ with a = 12.268 ( 2), b = 9.916 (3), c = 12.625 (2) Á, ß = 91.79 (1)°, and Z = 2. The monocyclic derivative 3 crystallizes in the monoclinic space group P2fc with a = 20.114 ( 6), b = 9.554 (2), c = 17.178 (3) ,ß= 114.24 (2)°, and Z = 4. Phosphorane 4 crystallizes in the triclinic space group PI with a = 9.690 (2), b = 15.414 (4), c = 21.350 (5) Á, a = 93.07 (2)°, ß = 90.17 (2)°, y = 99.97 (2)°, and Z = 4. The final conventional unweighted residuals are 0.056 (1), 0.039 (2), 0.038 (3), and 0.076 (4). Supplementary Material Available: Tables of thermal parameters, additional bond lengths and angles, hydrogen atom parameters (Tables S1-S3 for 1, Tables S4-S6 for 2, Tables S7-S9 for 3, and Tables S10-S12 for 4), and atomic coordinates (Tables S13-S16 for 1-4, respectively) (39 pages). Ordering information is given on any current masthead page.
